1. Field of the Invention
This invention relates to a process for the separation and the recovery of 3-methyl-3-butene-1-ol which is formed, as a by-product, during the production of isoprene by the reaction of isobutene and formaldehyde.
2. Description of the Prior Art
It is well known that 4,4-dimethyl-1,3-dioxane (useful as an intermediate for the production of isoprene) may be synthesized by the Prins reaction wherein isobutene is condensed with formaldehyde in an aqueous medium in the presence of an acid catalyst such as sulfuric acid, phosphoric acid or sulfonic acid at a temperature of 20.degree. to 100.degree.C. Such a method is described in, for example, U.S. Pat. No. 2,997,480. It is also well known that the above dioxane decomposes in the presence of acidic catalysts to give isoprene as described in, for example, U.S. Pat. Nos. 3,060,239 and 3,221,075 and British Pat. No. 884,809. In the production of isoprene by the reaction of isobutene and formaldehyde through the intermediate 4,4-dimethyl-1,3-dioxane as mentioned above, 3-methyl-3-butene-1-ol is formed as a by-product.
Since the boiling point of 3-methyl-3-butene-1-ol (boiling point: 130.degree.-131.degree.C.) is very close to that of 4,4-dimethyl-1,3-dioxane (boiling point: 133.degree.C.), it is difficult to separate them and recover said alcohol from said dioxane by a conventional distillation operation. Therefore, in the production of isoprene by the above method, the by-product 3-methyl-3-butene-1-ol inevitably accompanies the 4,4-dimethyl-1,3-dioxane cycled in the reaction system and both are converted to isoprene according to the following equations: ##EQU1##